*4.4. Study on the Impact of the Power Control Strategy Used in a PV Power Plant on the Resources Available for VPP*

Section 3.2 discusses the relationship between active power and reactive power applied to low voltage generation units. It has been shown that such generating units have a standard *cos*ϕ*(P)* characteristic assuming a reactive power consumption for the production of active power above 50% of the maximum power of the generating unit. This regulation strategy serves to reduce of voltage increase. However, from the point of view of the virtual power plant, the regulation introduces certain restrictions which affect the availability of resources integrated into the VPP. In order to highlight this issue, studies of PV power plants belonging to the VPP were carried out. The PV power plant mentioned is a 132 kW PV installation marked as PV-C in Figure 4 and Table 2. This power plant is the facility consisting of several individual photovoltaic power plants PV, three-phase and single-phase installations using different installed power and different photovoltaic technologies but all connected in the same PCC. From a PCC point of view, the combined phase is occupied almost symmetrically but there may be some differences between the phases. The aim of the presented studies is to determine the level of energy, which is redirected to the reactive power consumption instead of the active power generation. In order to achieve this, the actual measurement of changes in active and reactive

power in the selected week, which is characterized by similar daily weather conditions, was analyzed. Changes in active and reactive power during the test week due to changes in solar irradiance are shown in Figure 13. It can be seen that a high level of active power generation is accompanied by reactive power consumption, which indicates that PV installations integrated with the PV power plant realize the *cos*ϕ*(P)* characteristic. In order to emphasize the observed correlation, Figure 14 shows the correlation between solar irradiation and active and reactive power. The calculated Pearson correlation coefficients for active and reactive power confirm the high correlation between solar irradiation and the generation of active power and, consequently, reactive power consumption.

**Figure 13.** Changes in active (PL1, PL2, PL3) and reactive (QL1, QL2, QL3) power in specific phases in point of common coupling (PCC) of PV power plant PV-C and changes in solar irradiation in the examined week.

**Figure 14.** Correlation analysis between solar irradiation and active power (**a**) and reactive power (**b**) in PCC of PV power plant PV-C during the investigated week.

Table 5 contains an analysis of active power generation and reactive power consumption over one week to determine the effect of the implemented *cos*ϕ*(P)* characteristic on the reduction of active power generation availability. It was shown that during one observation week, which is characterized by sunny weather, the total amount of active energy produced is 4799.91 [kWh] and at the same time, reactive energy consumed is 53.87 [kvarh]. This leads to the conclusion that during the sunny week

1.11% of the total energy from the considered PV is not available for the VPP planning because it is used for reactive power regulation. The result presented corresponds to a sunny week, therefore a long-term analysis should be carried out to verify this observation.

integrated into the VPP in the perspective of the observed week. **Parameter Phase L1 Phase L2 Phase L3 Total** Time of active power generation 92.17 [h] 93.17 [h] 87.50 [h] 90.95 [h] (mean) [h]/[% 168 h of the week] 54.86 [%] 55.46% [%] 52.08 [%] 54.13 [%] (mean) Time of reactive power consumption 52.33 [h] 51.50 [h] 38.00 [h] 47.28 (mean)

[h]/[% 168 h of the week] 31.15 [%] 30.65% 22.62 [%] 28.14 [%] (mean) Generated active energy 1666.51 1509.35 1624.05 4799.91 [kWh] [kWh]/[% of total energy] 98.89 [%] Consumed reactive energy 34.18 14.14 5.55 53.87 [kvarh] [kvarh]/[% of total energy] 1.11 [%]

**Table 5.** Analysis of energy production of the PV power plant during the investigated week in order to determine the impact of reactive power regulation on reducing the availability of the resources
